1. Field of the Invention
The present invention relates to nonradiative planar dielectric lines used in a millimetric wave band or a microwave band. The invention is also concerned with integrated circuits using the above dielectric lines.
2. Description of the Related Art
Microwaves and millimetric waves are electromagnetic waves having a very wide frequency range from 300 MHz to 300 GHZ and are finding widespread use not only in various types of radar, relay, such as ground long-distance calls, television broadcasting waves, and satellite communication, but also satellite broadcasting and mobile communication. Meanwhile, research and development is being actively conducted to form integrated circuits, such as monolithic microwave integrated circuits (MMICs). Thus, the miniaturization of apparatuses utilizing electromagnetic waves in a microwave or millimetric wave band is progressing rapidly, and the range of the use of the electromagnetic waves in the above bands is expanding.
Hitherto, in a microwave or millimetric wave band, transmission lines formed by disposing predetermined electrodes on a dielectric substrate, such as not only waveguides and coaxial lines, but also microstrip lines, coplanar lines, and slot lines, are primarily used. The waveguides are employed for the parts where low transmission losses are required, while the coaxial lines are used as connecting cables between apparatuses. Further, largely, the microstrip lines and the slot lines are used to connect electronic components, since it is easy for them to be connected with electronic components, such as ICs.
A slot line is configured, as shown in FIG. 15, in such a manner that electrodes 421a and 421b are formed with a predetermined gap on the upper surface of a dielectric substrate 423 having a predetermined thickness h400. This makes it possible to form a slot 424 having a predetermined width W400 between the electrodes 421a and 421b. In the slot line configured as described above, electromagnetic waves propagate in the longitudinal direction of the slot 424 while forming a mode having an electric field parallel to the width of the slot 424 and a magnetic field H400 parallel to the length of the slot 424, as shown in FIG. 15.
As the transmission line, not only the above types of lines, but nonradiative dielectric lines (NRD guides) are used. The NRD guide is formed by providing a rectangular-prism-shaped dielectric strip between two conductive plates, and exhibits the characteristics of low transmission losses.
However, the foregoing known lines utilizing electromagnetic waves in a millimetric wave or microwave band present the following problems. The waveguides are large, and an apparatus using a waveguide is thus difficult to miniaturize. It is also difficult for the waveguides to be connected to electronic components, such as ICs. Moreover, in the coaxial lines, unwanted high-order modes are generated at frequencies higher than a specific frequency, which is determined by the shape of the cross section of the coaxial line, thereby increasing transmission losses. This makes the coaxial line unusable. Accordingly, if it is desired that the coaxial line be used at a frequency in a millimetric wave band, around 60 GHz, the diameter of the coaxial line should be reduced to as low as 1 mm. This makes it difficult to manufacture the coaxial line. Further, the microstrip lines, the coplanar lines, and the slot lines have high transmission losses, and thus, they are not suited in the use for the parts where low transmission losses are required. Additionally, it is not easy for the conventional NRD guides to be connected to electronic components, such as ICs.
To solve the above problems, the same assignee assigned to the invention of this application has filed a patent application concerning the planar dielectric line and the integrated circuit using the same line in Japanese Patent Application No. 07-069867.